boy…..there is not too many classics in my opinion but i’ll give you some links as to my personal faves.
http://g.e-hentai.org/g/741307/f676bf2b7b/
^ in spanish but its animated. very good though
http://g.e-hentai.org/g/809409/7311eaad7f/
http://g.e-hentai.org/g/577451/ff211d6086/
^ gender bent hidan
http://g.e-hentai.org/tag/artist:sahara+wataru
^ the works of sahara wataru
http://g.e-hentai.org/tag/group:blue+syndrome
^ ninja dependence series(warning: very dark)
those are my personal faves. matt wilson has done tons of stuff and of course there is naruhodo.